Step 1: You Might Be Surprised How Cheap It Can Be
A typical resistance Spot-Welder can range in price from about $200-$800, but with a little resourcefulness, and a bit of free time, you can make one like this for about $10 or less.
Spot welders are used to fuse thin sheets of metal together. They are most likely used in the auto industry, as well as HVAC for welding metal ducting.
There are a couple of videos you should see before starting on this project, because you may want some background on how the device works.
Here is how to: Make The Metal Melter
Here is what it can do: The Metal Melter
Step 2: Take Some Measurements
I found a 6' length of 1x6 common board for about $4, which actually measures out at 5-1/2", so it will work just fine.
Two pieces of the board will need to be cut to 12" lengths (5-1/2" x 12"), but the rest can be pushed through a table saw to trim the width down to 4-1/2" (1/4" wider than the transformer base).
Step 3: Roughing The Case Together
4" x 4-1/2"
12" x 4-1/2"
24" x 4-1/2"
The other 2 pieces of the common board should measure;
12" x 5-1/2" (x 2 pieces)
You'll also need 4 pieces of 2x2 measuring;
2" x 2" x 13-1/2" (x 2 pieces)
2" x 2" x 4" (x 2 pieces)
This is all the wood you'll need for building the casing.
I used a 3/4" rounding bit and my router to smooth the edges and give it a cleaner look.
This is roughly how it will look when it's assembled.